Murine models of cancer now have an essential role in formulating modern concepts of carcinogenesis and metastasis, and provide us with a realistic means of developing and evaluating new diagnostic and therapeutic techniques. Moreover, transgenic and knock-out techniques for manipulating the genome allow us to tailor animal models that accurately recapitulate human tumorigenesis as well as cancer biology and its genetic underpinnings. With the ever-increasing number and importance of human disease models, particularly in the smaller animals such as mice and rats, the potential of high-resolution nuclear medicine technologies to contribute unique information is becoming apparent to many researchers. The critical advantage of nuclear medicine procedures is that they allow functional information to be obtained noninvasively, so each animal can be studied repeatedly. Thus, it is clear that nuclear medicine imaging of small animals is highly desirable. For these reasons, nuclear imaging techniques (such as SPECT) are becoming powerful new tools in imaging biological processes in small laboratory animals. However, the demands on small animal radionuclide imaging for these applications are significant. The radionuclide imaging system must offer spatial resolution in the range of 1-2 mm or better, and with excellent detection efficiency so that the study can be completed in reasonable time with small amounts of radioactivity and with radiation doses that do not perturb the biological model. The goal of the proposed research is to investigate a novel detector design to build a high performance small animal SPECT system.